JP5248112B2 - Method for forming a seal between a capacitive sensor housing and a diaphragm - Google Patents

Description

  The present invention relates to a capacitive pressure transducer. More particularly, the present invention relates to an improved method for forming a seal between a capacitive pressure transducer housing and a diaphragm.

  FIG. 1A shows a cross-sectional view of a conventional capacitive pressure transducer assembly 10 after assembly. 1B is an exploded view of the upper housing 40, the diaphragm 56, and the lower housing 60 of FIG. 1A. Briefly, the capacitive pressure transducer assembly 10 includes a body that defines an internal cavity. A relatively thin and flexible ceramic diaphragm 56 divides the internal cavity into a first sealed internal chamber 52 and a second sealed internal chamber 54. As described in detail below, the diaphragm 56 is attached so that the diaphragm 56 bends, moves, or deforms in response to the pressure difference between the chambers 52, 54. The transducer assembly 10 provides a parameter that represents the degree of curvature of the diaphragm, and thus this parameter indirectly represents the pressure difference between the chambers 52, 54. The parameter provided by the transducer assembly 10 that represents the pressure differential is the capacitance between the diaphragm 56 and one or more conductors disposed in the upper housing 40.

  The capacitive pressure transducer assembly 10 includes a ceramic upper housing 40, a ceramic diaphragm 56 and a ceramic lower housing 60. The upper housing 40 is generally cylindrical when viewed from above, and has an upper surface 41, a central lower surface 47, an annular shoulder 42 having a lower surface 42 a, and the central lower surface 47 and the annular shoulder 42. An annular channel 43 is formed. The lower surface 42 a of the annular shoulder 42 is substantially flush with the central lower surface 47. The upper housing further includes a pressure tube 44 that forms a central opening 48 (or passage) extending from the upper side to the lower side through the housing 40. The metal conductor 46 is disposed on the central portion of the lower surface 47.

  The diaphragm 56 is generally a circular thin diaphragm having an upper surface 57 and an opposite lower surface 59. A metal conductor 58 is disposed at the center of the upper surface 57 of the diaphragm 56. The diaphragm 56 and the upper casing 40 are arranged such that the conductor 46 of the upper casing 40 is placed opposite to the conductor 58 of the diaphragm 56. The diaphragm 56 is coupled to the upper housing 40 by an airtight seal (or joint) 70 described in detail below. The seal 70 is located between the lower surface 42 a of the annular shoulder 42 of the upper housing 40 and the corresponding annular portion of the surface 57 of the diaphragm 56. Once sealed, the reference chamber 52 is formed by the upper housing 40, the seal 70 and the diaphragm 56. An opening 48 in the pressure tube 44 provides an inlet or inlet path to the reference chamber 52.

  The generally circular lower housing 60 forms a central opening 64 and an upwardly projecting annular shoulder 62 having an upper surface 62a. The upper surface 62 a of the shoulder 62 of the lower housing 60 is coupled to a corresponding portion of the lower surface 59 of the diaphragm 56 by an airtight seal (or joint) 76. The seal 76 can be placed and incorporated in a manner similar to the seal 70. When sealed, the process chamber 54 is formed by the lower housing 60, the seal 76, and the surface 59 of the diaphragm 56.

  A pressure tube 66 having an inlet passage 68 is coupled to the lower housing 60 such that the inlet passage 68 is aligned with the opening 64 of the lower housing 60. Accordingly, the process chamber 54 is in fluid communication with the external environment via the opening 64 and the inlet passage 68. In operation, the capacitive pressure transducer assembly 10 measures the pressure of this external environment.

The conductors 46, 58 of the capacitive pressure transducer assembly 10 form a parallel plate of the variable capacitor C. As is well known, C = Aε _r ε ₀ / d, where C is the capacitance between the two parallel plates, A is the common area between the parallel plates, and ε ₀ is the vacuum dielectric constant. Ε _r is the relative permittivity of the material separating the parallel plates (eg, ε _r = 1 for vacuum), and d is the axial distance between the parallel plates (ie along the normal of the parallel plates) Measured distance between parallel plates). Thus, the capacitance provided by capacitor C is a function of the axial distance between conductor 46 and conductor 58. In accordance with the change in the pressure difference between the chambers 52 and 54, the diaphragm 56 moves up and down or curves, so that the capacitance provided by the capacitor C also changes. At any point in time, the capacitance provided by the capacitor C represents the instantaneous pressure difference between the chambers 52, 54. Using a known electrical circuit (eg, a “tank” circuit characterized by a resonant frequency that is a function of the capacitance provided by capacitor C), the capacitance provided by capacitor C is measured to represent the pressure difference. An electrical signal can be generated. The conductors 46, 58 can be constructed from a wide range of conductive materials such as gold or copper, for example, and can be manufactured by known thin film or thick film processes or other known manufacturing methods. When a thin film process is utilized, the conductors 46, 48 may have a thickness of about 1 μm, for example.

  Diaphragm 56 is often made from mixed aluminum oxide. However, other ceramic materials such as a glass ceramic single crystal oxide material may be used. Capacitance sensors having ceramic components are disclosed in US Pat. Nos. 5,920,015 and 6,122,976.

  In operation, the capacitive pressure transducer assembly 10 is generally used as an absolute pressure transducer. In this configuration, the reference chamber 52 is generally evacuated first by connecting a vacuum pump (not shown) to the pressure tube 44. After the reference chamber 52 is evacuated, the tube 44 is then sealed to maintain a vacuum in the reference chamber 52. In addition, a “getter” can be coupled to the tube 44 to maintain the vacuum in the reference chamber for an extended period of time. This creates a “reference” pressure in the chamber 52. Vacuum is a convenient reference pressure, but other reference pressures can be used. After the reference pressure is generated in chamber 52, pressure tube 66 can then be connected to a fluid source (not shown) to measure the pressure of this fluid. By coupling the pressure tube 66 in this manner, the fluid whose pressure is to be measured is sent to the process chamber 54 (and the lower surface 59 of the diaphragm 56). The center of the diaphragm 56 moves up or down in accordance with the pressure difference between the chambers 52 and 54, whereby the capacitance of the capacitor C changes. Because the instantaneous capacitance of capacitor C represents the position of diaphragm 56, transducer assembly 10 can measure the pressure in chamber 54 relative to the reference pressure generated in chamber 52.

  Of course, the transducer assembly 10 can also be used as a differential pressure transducer. In this configuration, the pressure tube 44 is connected to a first fluid source (not shown) and the pressure tube 66 is connected to a second fluid source (not shown). The transducer assembly 10 can then measure the differential pressure between the two fluid pressures. Alternatively, a “gauge” transducer can be realized by maintaining the reference chamber 52 at atmospheric pressure.

  As described above, a change in pressure difference between the chambers 52, 54 causes the diaphragm 56 to bend, thereby changing the gap between the conductor 46 and the conductor 58. By measuring the change in the gap, the pressure difference can be measured. However, the gap may be affected by factors that are independent of pressure. For example, the gap can be affected by temperature changes. Because the components of the transducer assembly 10 can be made from a wide variety of materials, each having a unique coefficient of thermal expansion, temperature changes in the surrounding environment cause the diaphragm 56 to move toward or away from the conductor 46. there is a possibility. Advantageously, the change in gap due to temperature changes has different characteristics than the change in gap due to changes in pressure differential. It is known to include a second conductor (not shown) disposed adjacent to the conductor 46 on the lower surface 47 of the upper housing 40 in order to compensate for the change in gap caused by changes in the ambient environment temperature. ing. In such an embodiment, conductors 46 and 58 form a parallel plate of variable capacitor C1, and conductor 58 and the second conductor form a parallel plate of variable capacitor C2. Two capacitors C1, C2 can be used in a known manner to reduce the sensitivity of the transducer to temperature changes.

  The upper housing 40 has a surface parallel to the surface formed by the conductor 58 (ie, the diaphragm 56) when the lower surface 47 and any conductor placed thereon are equal in pressure in the chambers 52, 54. Aligned to be placed on. As described above, the capacitance formed by the conductors 46, 58 depends on the gap (ie, the axial distance) that exists between these opposing conductors. The gap is relatively small (for example, about 0.0004 inch (10 to 12 μm)), in part, the thickness of the seal 70 and the shape and configuration of the upper housing 40 (for example, the amount by which the lower surface 42a deviates from the plane, that is, If there is, it depends on the displacement with respect to the lower surface 47).

  A method of forming seals 70 and 76 is disclosed in US Pat. No. 6,122,976. In this method, a seal is formed by placing solid glass beads between two faces, followed by melting the sealing beads. Upon melting, the molten beads flow into the space between the two faces. Upon cooling, the flowed sealed bead material forms a seal between the two faces.

  FIG. 2 shows a bottom view of the upper housing 40 of FIGS. 1A and 1B. According to the teaching of US Pat. No. 6,122,976, glass particles are mixed with an adhesive and a solvent to form a paste material. Next, the paste material has a pattern of sealing beads 72 on the surface on which the seal is formed, for example, on the lower surface 42 a of the shoulder 42 of the upper housing 40 and the upper surface 62 a of the shoulder 62 of the lower housing 60. Set as. The pattern of sealing beads 72 can be placed and formed on the surface utilizing a suitable screen printing or pad / brush printing deposition process. As described in detail below, the sealing beads 72 are placed such that there are open channels 78 between the sealing beads 72. After the pattern of sealing beads (paste) 72 is placed on the surface, sealing beads 72 undergo a drying process, a “burn-off” process, and a subsequent pre-melt / sinter process. In each subsequent step, the sealing bead 72 is exposed to a gradually increasing high temperature. For example, the sealing beads 72 are heated to 100-150 ° C. during the drying process, heated to 325-375 ° C. during the melting process, and heated to 490-500 ° C. during the pre-melting / sintering process. The The deposited sealing beads (paste) 72 is cured in a drying process and can withstand processing. During the burn-off process, some of the solvent and adhesive is burned out of the paste. If the burn-off process is not performed correctly, the seal will not be impervious and will be structurally incomplete. When the sealing bead 72 is fully degassed (burned off), the temperature is further increased and the premelting / sintering process is performed. During the premelting / sintering process, the glass particles present in the beads 72 melt together. However, the beads 72 do not flow into the open channel 78 during the pre-melt / sinter step. After the premelting / sintering step, the sealing beads 72 are cooled. After cooling, the sealing beads 72 can be mechanically processed, such as polished, to have a desired height. Depending on the application, the desired height of the (non-melting) sealing bead 72 can be formed, for example, to about 20-24 μm.

  The pattern in which the beads 72 are placed (shown in FIG. 2) affects the ability of the beads 72 to completely degas while the seal 70 (or seal 76) is formed. In order to facilitate degassing of the sealing beads 72, it is advantageous to place the sealing beads 72 with channels 78 between the sealing beads 72. The cross-sectional dimensions of the sealing bead 72 and the channel 78 placed between the beads are selected to achieve the desired degassing effect. In one exemplary embodiment, the sealing bead 72 has a diameter of 0.1 to 0.5 mm and the channel 78 has a width of approximately the same dimensions.

  After the sealing bead 72 is placed and prepared on the lower surface 42a and the upper surface 62a as described above, the diaphragm 56 is sealed with the sealing bead 72 placed on the lower surface 42a. The lower casing 60 is aligned with the upper casing 40 so as to be in contact with the sealing area of the upper surface 57, and the sealing beads 72 placed on the upper surface 62 a are sealed with the lower surface 59 of the diaphragm 56. The diaphragm 56 is aligned so as to be in contact with the stop region. Next, a compressive force is applied to the upper housing 40, the diaphragm 56 and the lower housing 60 substantially perpendicularly to the direction of the diaphragm 56. Next, a high temperature (ie, higher than the temperature applied during the pre-melting / sintering step) is applied to melt the sealing beads 72. When melted, the sealing beads 72 flow and flow between the shoulder 42 of the upper housing 40 and the upper sealing region of the diaphragm 56 and between the shoulder 62 of the lower housing 60 and the lower sealing region of the diaphragm 56. Fills voids (ie, channels) that exist between them. When cooled, the sealing beads 72 thus form hermetic seals 70, 76 located between the diaphragm 56 and the upper housing 40 and the lower housing 60, respectively. In order to form a seal 70 (and seal 76) having a desired height (ie thickness) and area, the cross-sectional area and height of the unmelted sealing bead 72 is such that the total volume of sealing bead 72 material is desired. It is set to be sufficient to form a seal 70 (ie, the total volume of sealing beads 72 is approximately equal to the volume of the desired seal 70).

  If the conductors of a positive displacement transducer cannot be accurately aligned and oriented with respect to each other, the performance characteristics of the positive displacement transducer will be adversely affected. For example, if the gap between the opposing conductors 46, 58 is not controlled and formed with strict dimensional tolerances, the positive displacement transducer will have unacceptable performance characteristics. Furthermore, if the gap is not controlled to be constant, it becomes difficult to manufacture a large number of transducers, all having the same performance characteristics.

  The sealing method described above does not necessarily guarantee that the formed seal 70 has an accurate and constant thickness. For example, if an excess or insufficient amount of sealing bead 72 material is used to form the seal 70, the seal 70 may be too thick or too thin. Also, if the compressive force applied between the upper housing 40 and the diaphragm 56 during the melting and cooling steps is not uniform, the thickness of the seal 70 may not be constant.

Accordingly, there is a need for a method for forming a seal between the housing of a positive displacement pressure transducer and a diaphragm with high accuracy.
US Pat. No. 5,920,015 US Pat. No. 6,122,976

  The present invention relates to a method and system for forming a seal between a housing of a capacitance pressure transducer and a diaphragm with high accuracy. In certain capacitance pressure transducers, the axial distance between the opposing conductors of the capacitance pressure transducer depends in part on the thickness of the seal placed between the housing and the diaphragm. As described herein, high temperature and low temperature sealing beads are utilized to form a seal with an accurate and constant thickness. By utilizing an accurate and constant thickness seal, the opposing conductors of the capacitive pressure transducer can be accurately aligned and oriented with respect to each other during the manufacturing process.

  In one method, the high temperature sealing bead height is set to a known height. Next, the low temperature sealing beads are placed around the beads between the high temperature sealing beads. Next, the low temperature sealing beads and the high temperature sealing beads are sufficient to melt the low temperature sealing beads, but are insufficiently exposed to temperature to melt the high temperature sealing beads. Melted cold sealed beads flow around unmelted hot sealed beads. When solidified, the low temperature seal beads and the high temperature seal beads combine to form a seal. Since the high temperature sealing beads do not melt during the seal manufacturing process, the seal thickness can be set by controlling the height of the non-melting high temperature sealing beads. In the finished seal, the low temperature sealing beads that melt and flow during the manufacture of the seal have been transformed into a low temperature material that is conformally placed around the high temperature sealing beads. “Conformally arranged” means that the low temperature material flows around the high temperature sealing beads, such that the voids in the low temperature material are entirely limited and filled by the high temperature sealing bead material. . However, some unfilled voids may exist in the low temperature material (eg, the interface between the high temperature sealing bead and the low temperature material). It is desirable to avoid the formation of such voids, but as long as the voids are small enough and the number of voids is small enough, the presence of voids does not compromise the integrity of the seal and the low temperature material is around the high temperature sealing beads. It does not mean that they are not arranged conformally.

  Various objects, features and advantages of the present invention can be more fully understood with reference to the following detailed description of the invention when considered in conjunction with the following drawings. In the drawings, like reference numerals identify like elements. The following drawings are for illustrative purposes only and are not intended to limit the present invention. The scope of the present invention is set forth in the following claims.

  The present invention relates to a method and system for forming a seal between a housing of a capacitance pressure transducer and a diaphragm with high accuracy. The present invention provides a method for forming a fluid-tight seal having an accurate, uniform and constant thickness utilizing high temperature and low temperature sealing beads. By forming a seal with a controlled thickness, the axial distance between opposing conductors can be accurately controlled.

  FIG. 3 shows a cross-sectional view of an exemplary capacitive pressure transducer assembly 100 constructed in accordance with the present invention. Similar to the conventional capacitive pressure transducer assembly 10, the assembly 100 includes an upper housing 40, a diaphragm 56, and a lower housing 60. 3B is an exploded view of the upper housing 40, the diaphragm 56, and the lower housing 60 of the assembly 100 shown in FIG. 3A. Unlike the conventional transducer assembly 10, the assembly 100 includes an improved seal 170 that is placed between the diaphragm 56 and the upper housing 40. When sealed, the upper housing 40, the seal 70, and the diaphragm 56 form a reference chamber 152.

  Similarly, the improved seal 176 can be placed between the diaphragm 56 and the lower housing 60. When sealed, the lower housing 60, the seal 176, and the diaphragm 56 form a process chamber 154.

  The seal 170 is formed using high and low temperature sealing beads. High temperature sealing beads have a higher melting temperature than low temperature sealing beads. In order to achieve a high temperature sealing bead having a higher melting temperature than the low temperature sealing bead, the high temperature sealing bead and the low temperature sealing bead can be composed of different materials or have different amounts of common material.

  The formed seal 170 has an accurate and constant thickness. By utilizing a seal with an accurate constant thickness, the opposing conductors of the capacitive pressure transducer can be accurately aligned and oriented with respect to each other during the manufacturing process.

  FIG. 4 shows a plurality of high-temperature sealing beads 172 disposed on the lower surface 42 a of the shoulder 42 of the upper housing 40. As shown in the figure, the high temperature sealing beads 172 are uniformly distributed on the lower surface 42 a of the shoulder 42. The high temperature sealing bead 172 is composed of a glass material and is placed and processed in the same manner as the sealing bead 72 was placed (as described above in connection with FIG. 2). For example, the high temperature sealing bead 172 is placed by a printing process known in the art and then dried by applying heat. Thereafter, most of the solvent and adhesive contained in the high temperature sealing beads 172 are burned off by exposing the high temperature sealing beads 172 to high temperatures, and the high temperature sealing beads 172 are pre-melted by exposure to higher temperatures. / Sintered. After the pre-melting / sintering step, the high temperature sealing beads 172 are cooled and the high temperature sealing beads 172 solidify. The high temperature sealing bead 172 places the high temperature paste as a bead 172, exposes the bead 172 to a temperature increase of 40 ° C./min until it reaches 125 ° C., maintains 125 ° C. for about 15 minutes, Can be formed by exposing to a temperature increase of 40 ° C./min until reaching 720, maintaining 720 ° C. for about 10 minutes, and then decreasing the temperature at a rate of 40 ° C./min. The formed high temperature sealing bead 172 has a melting temperature of about 725 ° C.

  The high temperature sealing beads 172 do not melt (ie, do not flow in a liquid state) during the formation of the seal 170. Rather, the high temperature sealing bead 172 acts as a spacer that determines the thickness of the seal 170. In other words, the high temperature sealing bead 172 sets the thickness of the seal 170 by acting as a pedestal that extends between two surfaces that are sealed together. In order to achieve a seal 170 having an intended thickness (and a constant thickness), it is important that the high temperature sealing bead 172 has a bead height equal to the intended thickness. One simple way to ensure that the seal 170 has the desired thickness is to start with a high temperature sealing bead 172 that is thicker than the desired thickness of the seal 170. After the beads 172 are placed on the shoulder 42, the beads 172 are polished until the thickness (ie, height) matches the desired thickness of the seal 170. The desired thickness of the seal 170 may be, for example, 10 to 12 μm.

  In addition to the lapping / polishing technique, the height of the high temperature sealing bead 172 can also be generated by, for example, etching, reactive ion etching (dry etching) or laser cutting techniques known in the art. The height of the high temperature sealing bead 172 can be measured using, for example, drop indicator measurements, laser measurements, or target-capacitance measurement techniques known in the art.

  Referring now to FIG. 5, the high temperature sealing beads 172 are placed and formed on the lower surface 42a of the shoulder 42 to produce these bead heights. Next, low temperature sealing beads 174 are placed between and around the high temperature sealing beads 172 on the lower surface 42a. The low temperature sealing bead 174 has a lower melting point than the high temperature sealing bead 172. Advantageously, the cold sealed beads 174 are evenly distributed on the surface on which the beads are placed. Although the high temperature sealing bead 172 and the low temperature sealing bead 174 in FIGS. 4 and 5 are disposed and formed on the lower surface 42a of the shoulder 42 of the upper housing 40, the high temperature sealing bead is shown instead. The stop beads 172 and the low-temperature sealing beads 174 can be disposed and formed on the sealing region of the upper surface 57 of the diaphragm 56. Preferably, the low temperature sealing beads 174 are composed of a glass material and are placed and processed in the same manner (using different processing temperatures) as the high temperature sealing beads 172 as described above.

  The low temperature sealing beads 174 are placed between and around the high temperature sealing beads 172 leaving an open channel 178 between the low temperature sealing beads 174 and the high temperature sealing beads 172. Due to the presence of the open channel 178, the cold sealing bead 174 is properly degassed during the final sealing (melting and cooling) step. After the low temperature sealing beads 174 are placed (eg, after the drying, burn-off and pre-melting / sintering steps described above), the upper housing 40 and diaphragm 56 are compressed together and heated sufficiently to provide high temperature sealing. By melting the low temperature sealing bead 174 without melting the bead 172, a seal 170 is formed.

  As the low temperature sealing bead 174 melts, it forms a low temperature material and a portion of this material flows into the open channel 178 and fills the channel. Thus, the low temperature sealing bead 174 and the non-melting high temperature sealing bead 172 together form a seal 170. A proper amount (ie volume) of cold sealed bead 174 is placed on the shoulder 42 of the upper housing 40-simultaneously creating an open channel-so that when melted, the cold sealed bead 174 material (Along with the volume of the high temperature sealing bead 172) properly fills the space occupied by the seal 170. Therefore, it is desirable to ensure that the low temperature sealing bead 174 also has a specific bead height before melting the low temperature sealing bead 174.

  Thus, after the cold sealed beads 174 cool (ie, after the drying, burn-off and pre-melt / sinter steps), the bead height of each cold sealed bead 174 is measured and the target cold sealed bead height is measured. Compared with If the measured bead height of the low temperature sealing bead 174 exceeds the target low temperature sealing bead height, the low temperature sealing bead 174 is polished so that the height is equal to the target low temperature sealing bead height. To. In order to avoid obtaining a cold-sealed bead 174 having a bead height lower than the target cold-sealed bead height, advantageously, the cold-sealed bead 174 has a target cold-sealed bead height on the surface. Place with a bead height that exceeds. Because the cold seal bead 174 melts to fill the open channel 178, the target cold seal bead height is generally higher than the target hot seal bead height. The target cold sealing bead height can be, for example, twice the target hot sealing bead height.

  Reference is now made to FIGS. When the high temperature sealing bead 172 and the low temperature sealing bead 174 are disposed and formed on the lower surface 42 a of the upper housing 40, the diaphragm 56 is then connected to the shoulder of the upper housing 40. The upper casing 40 is aligned so as to extend from 42 to the sealing region of the diaphragm 56. In order to maintain the upper housing 40 in a proper relationship with the diaphragm, a compressive force F is applied between the upper housing 40 and the diaphragm 56 in a direction substantially perpendicular to the direction of the diaphragm 56. The compressive force F is obtained by placing a sufficient mass (ie, a weight body) on the upper surface of the upper housing 40 or applying a compressive force between the upper housing 40 and the diaphragm 56 using, for example, a press. Can be generated. Applying compressive force F ensures that when the low temperature sealing bead 174 melts, the low temperature sealing bead 174 flows into the open channel 178 and fills the channel, and the high temperature sealing bead 172 is at the top of the diaphragm 56. Ensures contact with surface 57.

  After the diaphragm 56 is aligned with the upper housing 40 (FIG. 6), the low temperature sealing bead 174 is exposed to a temperature higher than the melting point of the low temperature sealing bead 175 but lower than the melting point of the high temperature sealing bead 172. . Upon melting, the cold sealed beads 174 flow into the open channel 178 and fill the channel. When cooled, the previously melted low-temperature sealing bead 174 and high-temperature sealing bead 172 are integrated to form a seal 170 (FIG. 7). Since the temperature was maintained below the melting point of the high temperature sealing bead 172, the bead height h of the non-melting high temperature sealing bead 172 generates the thickness of the seal 170. Thus, by setting each of the bead heights h of the non-melting high-temperature sealed beads 172 to a constant height, the seal 170 can be accurately formed to have a uniform thickness. Furthermore, if the compressive force F is applied non-uniformly across the sealing area, the thickness of the seal 170 is adversely affected.

  FIG. 8 illustrates how the gap g (ie, axial distance) that exists between the conductors 46 and 58 of the capacitive pressure transducer assembly 100 depends in part on the thickness of the seal 170. Show. As described above, the lower surface 42a and the surface 47 of the upper housing 40 are substantially coplanar. The upper housing 40 is aligned so that the surface 47 of the upper housing 40 is parallel to the surface 57 of the diaphragm 56 when the pressures in the chambers 152, 154 are equal. When the pressures in the chambers 152, 154 are equal, the differential pressure acting on the diaphragm 56 is zero, so the diaphragm 56 is not subject to any deflection caused by the pressure. As is apparent in FIG. 8, when the pressures in the chambers 152 and 154 are equal, the gap g existing between the conductors 46 and 58 is determined from the thickness of the seal 170 (the bead height h of the high-temperature sealing bead 172). , 58 is obtained by subtracting the thickness.

  However, when a differential pressure is applied to the diaphragm 56, a part of the diaphragm 56 bends according to the differential pressure. Therefore, the gap g increases or decreases depending on the magnitude and direction of the differential pressure. For example, when the pressure in the process chamber 154 becomes higher than the pressure in the reference chamber 152, a part of the diaphragm 56 bends toward the surface 47 of the upper housing 40, and the gap g between the conductors 46 and 58 decreases. Conversely, when the pressure in the process chamber 154 becomes lower than the pressure in the reference chamber 152, a part of the diaphragm 56 bends away from the surface 47 of the upper housing 40, and the gap g between the conductors 46 and 58 increases. .

  Instead of providing a gap g that depends on the thickness of the seal 170 and the thickness of the conductors 46, 58, a capacitive pressure transducer assembly having a gap g approximately equal to the thickness of the seal 170 is advantageously realized. 9-11 illustrate a partial cross-sectional view of a capacitive pressure transducer assembly 200 having a gap g that is approximately equal to the thickness of the seal 170. The assembly 200 is similar to the assembly 100 except that the layer 246 is disposed on the lower surface 42 a of the shoulder 42 and the layer 258 is disposed on the upper surface 57 of the diaphragm 56. As can be seen in FIG. 9, the layers 246, 258 are disposed on the lower surface 42a and the upper surface 57, respectively, in the region where the seal 170 is formed. When sealed, the upper housing 40, the seal 170, the layers 246, 258, and the diaphragm 56 form a reference chamber 252. Layer 246 has a thickness approximately equal to the thickness of conductor 46, while layer 258 has a thickness approximately equal to the thickness of conductor 58. The layer 246 can be formed on the lower surface 42 a at the same time that the conductor 46 is formed on the lower surface 47, and can be made of the same material as the conductor 46. Similarly, layer 258 can be formed on top surface 57 at the same time that conductor 58 is formed on top surface 57 and can be composed of the same material as conductor 58. After layer 246 is placed on lower surface 42a of shoulder 42, high temperature sealing bead 172 (having bead height h) and low temperature sealing bead 174 are placed and formed on layer 264 by the techniques described above. can do.

  After the diaphragm 56 is aligned with the upper housing 40 (FIG. 9), a compressive force F is applied and then the low temperature sealing beads 174 are melted. Upon cooling, the previously melted low temperature sealing bead 174 and high temperature sealing bead 172 together form a seal 170 located between layers 246 and 258 (FIG. 10). As can be seen in FIG. 11, the thickness of the layers 246, 258 is approximately equal to the thickness of the conductors 46, 58 when the pressure is equal in the chambers 252, 154, respectively, so the gap g present between the conductors 46, 58 is It is approximately equal to the thickness of the seal 170. The thickness of the generated seal 170 is set by the bead height h of the high temperature sealing bead 172, so the gap g of the assembly 200 is approximately equal to the bead height h and is controlled by the bead height h.

  Layers 246, 258 can be composed of conductive or non-conductive materials. If conductive material is used, layers 246, 258 act as capacitive guards for conductors 46 and 58.

  The manufacturing tolerances of the upper housing 40 and diaphragm 56 to be manufactured are known in the art by forming a seal between such components using the present invention during the manufacture of these sensor components. Therefore, the axial distance between the counter electrodes can be established accurately and uniformly. By providing a seal 170 having an accurate, uniform and constant thickness, the present invention can be utilized to provide a transducer assembly having stable and reliable performance characteristics.

  The upper housing 40 of the assembly 100, 200 has a central lower surface 47 that is substantially flush with the lower surface 42a. In other capacitive pressure transducer assemblies, the central lower surface 47 of the upper housing 40 is offset from the lower surface 42a of the shoulder 42 by a slight distance. Therefore, if the pressure in the chamber on both sides of the diaphragm is equal, the gap g present between the conductors 46, 58 depends on the thickness of the seal 170 and the amount by which the surface 47 is offset from the lower surface 42a. However, since the same plane can generally be manufactured with a smaller tolerance compared to non-coplanar surfaces (eg, parallel but offset from each other), the central lower surface 47, which is substantially coplanar with the lower surface 42a, is formed. It is advantageous to use the upper housing 40 having it.

  The low temperature sealing bead 174 and the high temperature sealing bead 172 of FIGS. 4 and 5 are shown having a circular cross section, but the cross section of the low temperature sealing bead 174 and the high temperature sealing bead 172 is square, rectangular, rhombus Or it may be a parallel-epiped shape (e.g., with tips positioned in close proximity to each other), hexagonal, or a variety of other acceptable shapes. The cross sections of the low temperature sealing bead 174 and the high temperature sealing bead 172 need not be the same.

  The present invention has been described above in connection with a ceramic pressure transducer assembly in which the upper housing 40, diaphragm 56, and lower housing 60 are all made from a ceramic material (eg, aluminum oxide). However, other materials can be used without departing from the invention.

  Although various embodiments have been illustrated and described herein that incorporate the teachings of the present invention, those skilled in the art will readily devise many other various embodiments that incorporate these teachings. It is possible.

It is sectional drawing of the conventional electrostatic capacitance sensor. It is a partial expanded sectional view of the conventional electrostatic capacitance sensor of FIG. 1A. A method is shown in which sealing beads can be placed on the capacitive sensor housing and a seal can be formed between the housing and the diaphragm. 1 is a cross-sectional view of one embodiment of a capacitive sensor configured in accordance with the present invention. It is a partial expanded sectional view of the electrostatic capacitance sensor of FIG. 3A. FIG. 6 illustrates an exemplary method for placing high temperature sealing beads on a capacitive sensor housing. FIG. 6 illustrates an exemplary method for placing a low temperature sealing bead on a capacitive sensor housing. FIG. 6 illustrates one step in an exemplary method of forming a seal between a capacitive sensor housing and a diaphragm. FIG. 6 illustrates another step in an exemplary method of forming a seal between a capacitive sensor housing and a diaphragm. FIG. 3 is an enlarged view of an exemplary seal formed between a capacitive sensor housing and a diaphragm in accordance with the present invention. FIG. 6 illustrates one step in an exemplary method of forming a seal between a capacitive sensor housing and a diaphragm. FIG. 6 illustrates another step in an exemplary method of forming a seal between a capacitive sensor housing and a diaphragm. FIG. 3 is an enlarged view of an exemplary seal formed between a capacitive sensor housing and a diaphragm in accordance with the present invention.

Claims (31)

A method of forming a seal between a housing of a capacitive pressure transducer assembly and a diaphragm comprising:
Disposing a first set of beads on a sealing region, wherein the sealing region is either part of a housing or part of the diaphragm, and the first set of beads is a first melt. Having temperature characteristics;
Disposing a second set of beads on the sealing region, wherein the second set of beads has a second melting temperature characteristic, wherein the second melting temperature is lower than the first melting temperature; The first and second sets of beads are disposed on the sealing region such that a channel exists between adjacent beads;
Urging the housing and the diaphragm against each other such that at least a portion of the second set of beads is in contact with the housing and the diaphragm;
Heating the diaphragm and housing to a temperature between the first and second melting temperatures, thereby melting at least a portion of the second set of beads;
Cooling the diaphragm and housing to a temperature below the second melting temperature;
A method comprising:   The method of claim 1, wherein the diaphragm is composed of a ceramic material.   The method of claim 2, wherein the ceramic material comprises aluminum oxide.   The method of claim 1, wherein the housing is composed of a ceramic material.   The method of claim 1, wherein the first and second sets of beads are comprised of a glass material.   The method of claim 1, wherein the diaphragm and the housing are made of a ceramic material comprising aluminum oxide, and the first and second sets of beads are made of a glass material.   The method of claim 1, further comprising establishing that each bead in the first set has approximately the same bead height. Establishing that each bead of the first set has approximately the same bead height,
Measuring the bead height of each bead of the first set;
Comparing the measured bead height to a target bead height;
If the measured bead height exceeds the target bead height, polishing the beads to obtain the target bead height;
The method of claim 7 comprising :   The method of claim 1, wherein the biasing is caused by placing an additional weight on the capacitance pressure transducer.   The method of claim 1, wherein the bias is generated by an external force applied between the housing and the diaphragm. The method of claim 10 , further comprising continuing to apply and apply the external force to the diaphragm and housing until at least a portion of the first set of beads contacts the housing and the diaphragm .   The method of claim 1, wherein the first and second sets of beads are arranged by a printing process.   The method of claim 1, wherein each bead of the first set is composed of glass particles. Drying the arranged first set of beads;
Degassing at least a portion of any organic solvent and adhesive present in the disposed first set of beads;
Melting together at least some of the glass particles contained in each bead within each bead of the first set of beads;
Coagulating the first set of beads by cooling the first set of beads;
Measuring the bead height of each bead of the first set of beads;
Comparing the measured bead height of each bead of the first set of beads to a target bead height;
Polishing the beads in the first set of beads to the target bead height if the measured bead height exceeds the target bead height;
14. The method of claim 13, further comprising:   15. The method of claim 14, wherein each second set of beads is composed of glass particles. Drying the arranged second set of beads;
Degassing at least a portion of any organic solvent and adhesive present in the arranged second set of beads;
Melting within each bead of the second set of beads together at least a portion of the glass particles contained in each bead;
Coagulating the second set of beads by cooling the second set of beads;
Measuring the bead height of each bead of the second set of beads;
Comparing the measured bead height of each bead of the second set of beads to a second target bead height;
Polishing the beads in the second set of beads to a second target bead height if the measured bead height of the bead exceeds a second target bead height;
The method of claim 15, further comprising: A capacitive pressure transducer assembly comprising:
A body forming an internal cavity;
A first conductor disposed on the body;
A diaphragm disposed within the body, the diaphragm comprising a second conductor, the diaphragm dividing the internal cavity into a first chamber and a second chamber, wherein a portion of the diaphragm is part of the second chamber. Moving in a first direction in response to a pressure in the first chamber that is higher than a pressure in the first portion, the portion of the diaphragm is A diaphragm moving in a second direction opposite to the one direction;
The first and second conductors generate a capacitance, which represents a gap existing between a portion of the diaphragm and the first conductor;
A seal disposed between a portion of the body and a portion of the diaphragm;
With
The seal includes a first element at least partially surrounding a set of spacer elements;
The seal has a thickness approximately equal to the height of the spacer element;
The spacer element is coupled to at least part of the body or part of the diaphragm;
The first element has a first melting temperature characteristic;
The capacitance pressure transducer assembly, wherein the spacer element has a second melting temperature characteristic and the first melting temperature is lower than the second melting temperature.   The assembly of claim 17, wherein the diaphragm is electrically conductive and acts as the second conductor.   The assembly of claim 17, wherein the diaphragm is non-conductive and the second conductor is disposed on the diaphragm.   The assembly of claim 19, wherein the diaphragm is constructed from a ceramic material.   21. The converter of claim 20, wherein the ceramic material is composed of aluminum oxide.   The assembly of claim 17, wherein the body includes an upper housing and a lower housing, and the upper housing and the diaphragm form the first chamber.   24. The assembly of claim 22, wherein the upper housing is constructed from a ceramic material.   23. The assembly of claim 22, wherein the diaphragm and the upper housing are made of a ceramic material comprising aluminum oxide, and the first element and the set of spacer elements are made of a glass material.   18. The assembly of claim 17, wherein the first element and the set of spacer elements are comprised of a glass material.   The assembly of claim 17, wherein the transducer assembly is capable of measuring absolute pressure.   The assembly of claim 17, wherein the transducer assembly is capable of measuring gauge pressure.   The assembly of claim 17, wherein the transducer assembly is capable of measuring a differential pressure.   The assembly of claim 17, wherein the gap that exists between the portion of the diaphragm and the first conductor depends on the thickness of the seal.   30. The assembly of claim 29, wherein the gap is approximately equal to the thickness of the seal. The first conductor has a first thickness, the second conductor has a second thickness;
30. The assembly of claim 29, wherein the gap is approximately equal to a thickness of the seal minus the first and second thicknesses.

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